Article

Ecotoxicology

, Volume 21, Issue 3, pp 832-846

Assessment of toxicity and potential risk of the anticoagulant rodenticide diphacinone using Eastern screech-owls (Megascops asio)

  • Barnett A. RattnerAffiliated withPatuxent Wildlife Research Center, U.S. Geological Survey Email author 
  • , Katherine E. HorakAffiliated withU.S. Department of Agriculture, National Wildlife Research Center
  • , Rebecca S. LazarusAffiliated withPatuxent Wildlife Research Center, U.S. Geological Survey
  • , Karen M. EisenreichAffiliated withPatuxent Wildlife Research Center, U.S. Geological Survey
  • , Carol U. MeteyerAffiliated withU.S. Geological Survey, National Wildlife Health Center
  • , Steven F. VolkerAffiliated withU.S. Department of Agriculture, National Wildlife Research Center
  • , Christopher M. CamptonAffiliated withU.S. Department of Agriculture, National Wildlife Research Center
  • , John D. EisemannAffiliated withU.S. Department of Agriculture, National Wildlife Research Center
  • , John J. JohnstonAffiliated withU.S. Department of Agriculture, Food Safety and Inspection Service

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Abstract

In the United States, new regulatory restrictions have been placed on the use of some second-generation anticoagulant rodenticides. This action may be offset by expanded use of first-generation compounds (e.g., diphacinone; DPN). Single-day acute oral exposure of adult Eastern screech-owls (Megascops asio) to DPN evoked overt signs of intoxication, coagulopathy, histopathological lesions (e.g., hemorrhage, hepatocellular vacuolation), and/or lethality at doses as low as 130 mg/kg body weight, although there was no dose–response relation. However, this single-day exposure protocol does not mimic the multiple-day field exposures required to cause mortality in rodent pest species and non-target birds and mammals. In 7-day feeding trials, similar toxic effects were observed in owls fed diets containing 2.15, 9.55 or 22.6 ppm DPN, but at a small fraction (<5%) of the acute oral dose. In the dietary trial, the average lowest-observed-adverse-effect-level for prolonged clotting time was 1.68 mg DPN/kg owl/week (0.24 mg/kg owl/day; 0.049 mg/owl/day) and the lowest lethal dose was 5.75 mg DPN/kg owl/week (0.82 mg/kg owl/day). In this feeding trial, DPN concentration in liver ranged from 0.473 to 2.21 μg/g wet weight, and was directly related to the daily and cumulative dose consumed by each owl. A probabilistic risk assessment indicated that daily exposure to as little as 3–5 g of liver from DPN-poisoned rodents for 7 days could result in prolonged clotting time in the endangered Hawaiian short-eared owl (Asio flammeus sandwichensis) and Hawaiian hawk (Buteo solitarius), and daily exposure to greater quantities (9–13 g of liver) could result in low-level mortality. These findings can assist natural resource managers in weighing the costs and benefits of anticoagulant rodenticide use in pest control and eradication programs.

Keywords

Rodenticides Birds Clotting time Diphacinone Secondary poisoning